The present invention relates generally to the electrical, electronic and computer arts, and, more particularly, to optical waveguides.
An optical waveguide is a physical structure that directs (i.e., guides) electromagnetic waves in the optical spectrum. Optical waveguides can be used as components in integrated optical circuits or as a transmission medium in optical communication systems and are generally classified according to their prescribed characteristics, including, for example, geometry (e.g., planar or strip waveguide), material type (e.g., semiconductor, glass, etc.), modal structure (e.g., single-mode or multi-mode) and refractive index distribution (e.g., step or gradient index), among other factors.
Silicon waveguide structures are strongly polarized due, at least in part, to the geometry of the structure. Standard silicon waveguides often exhibit large polarization-dependent attenuation and delay, which result in polarization-dependent loss (PDL) and polarization-dependent wavelength (PDW) shift, respectively, in devices constructed using standard silicon waveguides. Thus, a polarization diversity circuit (PDC) is typically employed to mitigate such PDL and PDW shift. Unfortunately, implementation of certain components of a PDC, such as waveguide-type polarization splitters and polarization rotators, can be challenging at least in part because it is difficult to rotate the optical axis of a planar waveguide. Furthermore, the small size and/or shape of the structure itself create challenges in fabrication of the waveguide.